As a transmission device which increases or reduces the speed of a rotational driving force of an input shaft side and then transmits the rotational driving force to an output shaft side, for example, a transmission control device of a toroidal continuously variable transmission (toroidal CVT) disclosed in Patent Literature 1 is known. In the device disclosed in Patent Literature 1, a power roller retained between an input disc and an output disc is tilted so that a transmission ratio (transmission gear ratio) is continuously changed. The power roller is tiltably supported by a trunnion. The trunnion is displaced in a direction of a tilt motion axis so that the power roller is tilted. The trunnion includes a hydraulic (hydraulically actuated) cylinder mechanism. Hydraulic oil is supplied to the cylinder mechanism, and the cylinder mechanism advances or retracts a piston to cause the trunnion to be displaced in the direction of the tilt motion axis. The piston includes a hydraulic actuation device including a spool valve and a pump. The hydraulic actuation device supplies the hydraulic oil discharged from the pump to the cylinder mechanism, and causes the spool valve to select (switch) a flow direction of the hydraulic oil to be supplied to the cylinder mechanism. The cylinder mechanism advances or retracts the piston according to the flow direction of the hydraulic oil supplied to the cylinder mechanism. According to the advancement or retraction of the piston, the power roller is tilted, and the speed of the rotational driving force of the input shaft side is increased or reduced according to the tilt motion angle of the power roller.